The instant invention relates to formulations useful as anaerobic adhesives.
Anaerobic adhesives are well known and have been in commercial use for several years. Most anaerobic adhesives are compositions containing a monomer, or combination of monomers, which will polymerize under certain conditions but not under other conditions. Those conditions generally favoring polymerization include the absence of oxygen and, if a redox initiator is used, the presence of metal ions. Oxygen acts as a polymerization inhibitor, and metal ions act as polymerization promoters.
Consequently, these adhesives find optimal use in situations where they are pressed tight between two metal surfaces, such as between the threads of a bolt and nut. The close fit effectively removes oxygen, and the metal surface provides metal ions. This combination of conditions causes the adhesive to polymerize, and a strong bond results.
While a significant breakthrough in the technology of anaerobic adhesives was made through the introduction of urethane bonds as described in U.S. Pat. No. 3,425,988 (1969), this technology is limited to reacting monofunctional alkyl and aryl acrylate esters containing hydroxy and amino functional groups with polyisocyanates. In some instances, it is desirable to include polyfunctional compounds such as polyglycols, bisphenols and polyamines, in addition to the monofunctional alkyl and aryl acrylate esters. These polyfunctional compounds serve two major functions: (1) to modify the physical properties of the resin and (2) to remove the unreacted and toxic excesses of isocyanate compounds. The isocyanate compounds are used in excess to reduce the amount of volatile and toxic monofunctional alkyl or aryl acrylate esters. Because of the tendency for polyisocyanates and polyahls to form network polymers (gel), the stoichiometry of the preceding reactions is limited.
In view of the aforementioned deficiencies of conventional adhesives, it is very desirable to provide an anaerobic adhesive that possesses all of the advantages of the recently developed polyurethane adhesives but does not have the stoichiometric limitations of such adhesives.